Innovative developments for portable electronics devices, typically cellular telephone handsets and the like, have been carried out at a rapid pace, in aim to produce increasingly compact and highly functional mobile devices. Power supply voltage values range widely in electronic circuits and LSI which are built-in in these devices, and for this voltage conversion, it is vital to use a small-sized, high-efficiency switching system, dc-dc converter. This paper describes an ultralow-profile micro dc-dc converter module with thickness 1.3 mm, the world's first single package of inductor, capacitor, and control IC as an ultracompact, high-efficiency voltage converter. The key device that led to realization of this small power supply is a thin-film inductor employing thin-film magnetic core.